1. Field of the Invention
The present invention relates to a system and method for reading radiation images stored on storage layer radiation screens. More specifically, the present invention relates to a system and method for reading multiple storage layer radiation screens positioned on a rotating carousel.
2. Description of Related Art
A variety of storage layer radiation screens have been developed for recording radiation images created by exposing the screen to a radiation source, such as x-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays and ultraviolet rays. When radiation is passed through an object onto the screen, the radiation forms a latent radiation image on the screen by stimulating the storage layer. This latent radiation image can then be road by scanning the screen using a suitable electromagnetic wave radiation, such as visible light or infrared rays (hereinafter referred to as "stimulating rays"), which releases the radiation energy stored in the storage layer as a light emission. The light emitted from the storage layer is then detected and converted into data corresponding to the image. Elimination of the image stored in the storage layer may be accomplished by exposing the storage layer for a period of time to a suitable electromagnetic wave radiation.
One type of storage layer radiation screen stores the radiation image in the form of an electrical charge distribution at a photo semiconductor layer. An example of this type of storage layer is described in Journal of Applied Photographic Engineering 4 178-182 (1978). Another type of storage layer radiation screen employs a luminophore, such as a phosphorescent material, which becomes excited when exposed to radiation. When the luminophore is exposed to stimulating rays, such as visible light, the luminophore releases energy in the form of light, Examples of this type of storage layer are described in U.S. Pat. Nos. 3,859,527 and 4,346,295 which are incorporated herein by reference.
As described in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428, stimulable phosphors have been proposed for use as luminophores in radiation image recording and reproducing systems. According to these systems, a screen containing a layer of a stimulable phosphor is exposed to radiation which has passed through an object being imaged, such as a part of the human body. The screen is then scanned with stimulating rays, such as a laser beam, which causes the phosphors in the screen to emit light in proportion to the amount of radiation absorbed by the portion of the screen being scanned. The light emitted by the screen is then detected and converted into an electrical signal. The electrical signal is then used to reproduce the radiation image as a visible image.
Storage layer radiation screens, such as stimulable phosphor screens, generally include a layer of stimulable material dispersed in an appropriate binder material. When the storage layer is self-supporting, the storage layer may itself form the storage layer radiation screen. However, the storage layer radiation screen generally includes a layer of stimulable material which is placed on a suitable substrate. For example, stimulable phosphor screens generally include an adhesive layer for binding the phosphor layer to the substrate. Stimulable phosphor screens can also include a protective layer formed on the phosphor layer surface opposite the substrate for physically and chemically protecting the phosphor layer. Stimulable phosphor screens can also include a light-reflecting layer between the phosphor layer and the substrate to improve the sensitivity of the screen. Alternatively, stimulable phosphor screens can include a light-absorbing layer between the phosphor layer and the substrate to improve the sharpness of the image produced by the storage phosphor screen. Colored or white particles have also been included in the phosphor layer to improve the sharpness of the image obtained.
One particular application for radiation screens employing a storage layer, such as a stimulable phosphor, is in the area of dental radiography. Storage layer radiation screens have the significant advantage of requiring lower x-ray radiation levels to produce the radiation image. As a result, the amount of x-ray radiation that a patient is exposed to when a storage layer radiation screen is used is significantly reduced, thereby reducing the health risks associated with x-ray radiography. In addition, storage layer radiation screens can provide images with higher resolution than are provided by conventional dental x-ray films.
Storage layer radiation screens can be more expensive to produce than traditional dental radiation films and require a device to read the image stored on the screens. In order for storage layer radiation screens to replace traditional dental radiation screens, it is important that the storage layer radiation screens be reusable. It is also important that the screens be easy to use and read. Accordingly devices are needed which facilitate the rapid, user-friendly reading of radiation images stored on these screens.
Devices for reading storage layer radiation screens generally read only one screen at a time and are limited in the size of the screen that can be read. A need exists for a screen reading device which is capable of simultaneously reading multiple screens of the same or different sizes. A need also exists for a removable sample holder so screens can be loaded onto one or more sample holders while other screens are being read.
Devices for reading storage layer radiation screens are also generally designed to read the screen in a linear manner where a screen scanner is rastered back and forth across the screen in order to read the entire surface of the screen. Devices which read screens using a rastered scanning motion generally require a greater amount of time to read than traditional dental x-ray film which requires 300 seconds to process. A need therefore exists for a device which can read storage layer radiation screens at a rate comparable to the time required to read traditional dental x-ray film.